The present invention relates to a microwave plasma processing apparatus for producing plasma from processing gas by a microwave and processing a wafer or similar semiconductor substrate by the plasma.
In the semiconductor devices art, plasma processing technologies are extensively used for treating wafers or similar semiconductor substrates accurately. Among them, a microwave plasma processing apparatus using a microwave implements an inherently high plasma density and reduces processing time. Japanese Patent Publication No. 5-3734, for example, proposes an apparatus of the type having a waveguide and a plasma processing chamber. A microwave propagated through the waveguide is emitted into the plasma processing chamber in which a wafer or similar semiconductor substrate is positioned, thereby generating plasma in the chamber. Specifically, the microwave is radiated into the chamber on the basis of a microwave distribution which is set up in the waveguide and can be readily estimated by computation. Ideally, the plasma density distribution conforms to the microwave distribution emitted into the chamber. A method of controlling the microwave distribution in the waveguide is taught in, for example, Japanese Patent Laid-Open Publication Nos. 62-122217 and 4-84426.
The method taught in the above Laid-Open Publication No. 62-122217 chances or controls the microwave distribution in the waveguide by inserting a plurality of variable tuner rods into the waveguide. The method disclosed in the other Laid-Open Publication No. 4-84426 controls the microwave distribution by moving a variable deflection plate disposed in the waveguide. In any case, it has been customary to control the plasma distribution indirectly through the control over the microwave distribution in the waveguide.
However, controlling the plasma distribution through the control over the microwave distribution in the waveguide is not a direct implementation. With this kind of method, it is difficult to control the plasma distribution in a desired manner. Specifically, the plasma distribution in the processing chamber is determined by the distribution of microwave radiation which is, in turn, determined by the interaction of the microwave and the gas or gas plasma in the chamber. Stated another way, the plasma distribution depends on the gas to be used. Therefore, it is extremely difficult to control the plasma distribution only through the control over the microwave distribution in the waveguide.